Stabilization of processed photographic emulsions to high temperatures and humidities



Patented Nov. 9, 1948 STABILIZATION OF PROCESSED PHOTO- GRAPHICEMULSIONS TO HIGH TEM- PERATURES AND HUMIDITIES Harold D. Russell,Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., acorporation of New Jersey No Drawing. Application October 25, 1945,Serial No. 624,571

8 Claims.

This invention relates to photography and particularly to the rapidprocessing of photographic materials.

Photographic processing of the customary silver halide emulsions afterexposure includes the essential steps of development, fixing, washingand drying. Optional steps such as reduction toning, etc., may beincluded but are not essential to the formation of a photographic image.These essential steps consume an appreciable amount of time and in manycases the time required for completion of each step cannot be shortenedwithout harming the quality of the final picture.

Yackel U. S. application, Ser. No. 594,589, filed May 18, 1945,describes a rapid processing method according to which a developedsilver image is stabilized by treatment with a solution of a compoundwhich does not react with metallic silver and which forms a light-inertsilver complex. by reaction with undeveloped silver halide. Thestabilization bath is used only until the silver halide has beensubstantially completely converted to a complex with the stabilizingcompound and the complex is left in the emulsion layer, the layer beingdried without any further treatment, such as washing. While the methodof the Yackel application is satisfactory for the stabilization ofimages which are not to be stored under adverse conditions, it has thedisadvantage that the silver images tend to fade when stored underconditions of'high temperature and humidity. A further disadvantage isthat certain of the stabilizing agents such as thiosulfates tend tocrystallize on the surface of the photographic emulsion.

It is therefore an object of the present invention to provide a rapidprocessing method for silver halide emulsion layers which produce printsstable to high temperature and humidity. A further object is to preventcrystallization of the stabiliza- .tion agent on the emulsion layerduring or after stabilization by my method. Other objects Will appearfrom the following description of my invention.

These objects are accomplished by the technique described herein whichincludes stabilizing the image in the presence of a metal below silverand above osmium in the electromotive series, without washing the print.

7 According to the stabilizing process described in Yackel U. 5.application, Serial No. 594,589, a silver halide emulsion. preferably agelatino-silver halide emulsion is exposed in the usual way and is thendeveloped in the customary silver halide developing agent. If theemulsion is coated on a paper or other porous support, it is desirableto wipev the surface of the emulsion with a sponge, a

2 rubber roll, or other applicator wet with the developing solution sothat the paper support is not soaked with the developing solution. Afterdevelopment has taken place, the excess developing agent present on thesurface of the print is removed by any convenient means such as asqueegee and the print treated with a stabilizing solution. The purposeof the stabilizing agent is to make the undeveloped silver halidesubstantially incapable of further photo-sensitivity. The stabilizingagent must be a compound which does not react readily with metallicsilver and which forms a light-inert silver complex by reaction with theundeveloped silver halide in the emulsion layer. The resulting silvercomplex should be light-colored or transparent so that it does notinterfere with the viewing or printing of the final image.

Stabilizing agents described for this purpose in the Yackel application,Serial No. 594,589, are compounds containing doubly-bonded sulfur or anSH linkage, such as alkali metal and ammonium thiosulfates andthiocyanates, thiourea and thioglycolic acid. Additional stabilizingagents which I have found suitable for this process include thefollowing:

HlTI(|3 o sr'i om H1 Ioo Thiobarbituric acid HzNC-SNH4 Ammoniumdithiocarbumate HiC-C-N o-sn o2Ncs 2-Mercapto-4-methyl-5-nitrothiazoleCHaCN o-sn HCS/ 2-\lercapto4-methyl-thiazole HzNOSNH-NHCSNH2 Dithiobiurea HCN L-AminOmethyI-Z-mercapto imidazolc5-Amino-2-mercapto-1,3,4-thiodiazole C-SH2-Mercapto-S-amino-benzimidazole HS. H20 0 OH Thioglycolic acid 81H 0 ai l HiNO C-OH 6-Amino-2-thio-4-hydroxy-pyrimidine HzNSC-OSNH:

Dithio oxamide 0 (015930 SNHi Thio trimethyl acetamide CHzSHOHNHzC oOHHCl Cysteine hydrochloride H H cH3o-o HN o s Propylene thioureaCH3OSNH2 Tliioacetamide CHsCHzOSNHz Thiopropionamide HSCH2C ONHNHiThioglycolic hydrazide The essential feature of the present invention isthe stabilization with these agents in the presence of a metal belowsilver and above osmium in the electromotive series. The metals of thisclass include palladium, platinum, gold, iridium and rhodium (seeMellor, Modern Inorganic Chemistry, 1925, page 433). Suitable compoundsare gold chloride, palladium chloride, iridium sesquichloride andchloroplatinic acid (I-IzPtCls) These compounds may be present in thestabilizing bath or in the emulsion layer. When used in the stabilizingbath, suitable amounts are from 0.01 to 10 grams per liter. An amount ofthe order of 0.04 gram per liter of wet emulsion is suitable for use inthe emulsion.

My invention will be further illustrated by reference to the followingexamples.

Typical stabilizing solutions are represented by the following examples.

Example 1 Thiourea grams 40 Acetic acid milliliters 60 Gold chloridegram 1 Water to liter 1 Example 2 Thiourea grams 40 Gold chloride grams5 Citric acid grams 15 Sodium citrate grams Water to liter 1 Example 3Sodium thiosulfate grams 150 Sodium bisulfite grams Gold chloride gram 1A;-;.&L-L';-'-' L-';$.L-LLLLLL hi-kliiliter-n 1 The following exampleillustrates the incorporation of my compounds in the emulsion layer.

Example 6 To a gelatino-silver halide emulsion there was added justbefore coating 0.2 gram of gold chlorideper 5000 cc. of Wet emulsion.This emulsion was coated, developed and treated with a stabilizing bathsuch as those of Example 4 or Example 5 without the gold chloride. Acheck emulsion without the gold chloride was treated in the same wayafter processing and upon storage at 100 F. and relative humidity forsix days was found to bleach to a brownish-yellow image. The emulsioncontaining the gold chloride showed greatly improved resistance tobleaching under similar conditions.

The use of salts of metals below silver and above osmium in theelectromotive series to improve the heat and high humidity stability ofimages treated with alkali metal and ammonium thiocyanates is not a partof my invention but is the invention of William L. Brice as described inapplication, Serial No. 624,570 filed concurrently herewith, now PatentNo. 2,448,857, September 7, 1948.

I have found that while many of the stabilizing solutions describedherein are satisfactory when used on paper emulsions as regardscrystallization of salts on the prints, in certain cases, the

stabilizing agent crystallizes on the surface of the emulsion on drying.This is particularly true in the case of film emulsions coated ontransparent cellulosic supports and stabilized with thiosulfatesolutions. I have found that this crystallization may be prevented byincorporating certain hydroxy-substituted aliphatic amines in thestabilizing bath. The hydroxy aliphatic amine may be added to thethiosulfate solution and sufllcient acid then added to neutralize thesolution or they may be added as the amine thiosulfate, replacing all orpart of the ammonium thiosulfate. The amines do not increase thestability of the silver complex formed with the stabilizing agent orprevent the fading'of the silver image but are used only to preventcrystallization on the surface of the emulsion. 7

Suitable hydroxy aliphatic amines which I have used for this purpose areethanolamine, diethanolamine, triethanolamine, c-diethyla'mino ethylalcohol, trimethylolaminomethane, 2 amino-2- methyl-Lpr-opanol andZ-amino 2 methyl-1,3- propanedi-ol.

As in the case of the process described in Yackel application, SerialNo. 594,589, hardened emulsions must be used with the present process.Positive emulsions such as are used on photographic papers are generallyhardened and no further hardening treatment is required. However, inthecase of certain negative film emulsions, the emulsion mu'st behardened before stabilizirig ac cording to my invention. This can bedone with a formaldehyde hardening bath before or after development orin any other suitable way.

Although the emulsion may be immersed in the developing and stabilizingsolutions, I prefer merely to moisten the surface of the emulsion withthe solutions except in the case of films and plates. Thus in the caseof paper supports, moistening the surface of the emulsion only, preventsthe support from becoming Wet and the drying done is thereby greatlyreduced.

It will be apparent from the foregoing description of my invention thatall or a major part of the silver remains in the emulsion afterstabilization. This diners from the customary fixing and washing inwhich the intent is to remove the residual silver halide from theemulsion. The unexposed silver halide is converted to a complex with thestabilizing agent and it is desirable that this complex be as stable andpermanent as possible so that there is little fading or discoloration ofthe final image.

It will be understood that the examples and modifications includedherein are illustrative only and that my invention is to be taken aslimited only by the scope of the appended claims.

I claim:

1. A rapid process for the formation of an image in a hardened silverhalide photographic layer which comprises exposing said layer,developing it with a silver halide developing agent and stabilizing itin the presence of a metal below silver and above osmium in theelectromotive series, with a compound selected from the class consistingof compounds containing sulfur doubly bonded to a single carbon atom andSH linkages bonded to a carbon atom which does not react readily withmetallic silver and which forms a light-inert silver complex by reactionwith undeveloped silver halide, only until the silver halide has beensubstantially completely converted to a complex by reaction with saidcompound, leaving said complex in said layer and drying said stabilizedimage Without any further treatment.

2. A rapid process for the formation of an image in a hardened silverhalide photographic layer which comprises exposing said layer,developing it with a silver halide developing agent and stabilizing itin the presence of a chloride of a. metal below silver and above osmiumin the electromotive series, with thiourea, only until the unexposedsilver halide is substantially completely converted to a light inertsilver complex by reaction with the stabilizing material, and dryingsaid stabilized image without any further treatment.

3. A rapid process for the formation of an image in a hardened silverhalide photographic layer which comprises exposing said layer,developing it with a. silver halide developing agent and stabilizing itin the presence of a chloride of a metal below silver and above osmiumin the electromotive series with ammonium thiosulfate, only until theunexposed silver halide is substantially completely converted to a lightinert silver complex by reaction with the stabilizing material, anddrying said stabilized image without any further treatment.

4. A rapid process for the formation of an image in a hardened silverhalide photographic layer which comprises exposing said layer,developing it with a silver halide developing agent and stabilizing itin the presence of gold chloride, with ammonium thiosulfate, only untilthe unexposed silver halide is substantially completely converted to alight inert silver complex by reaction with the stabilizing material,and drying said stabilized image without any further treatment.

5. A rapid process for the formation of an image in a hardened silverhalide photographic layer which comprises exposing said layer,developing it with silver halide developing agent and stabilizing it bytreatment with a solution of a compound selected from. the classconsisting of compounds containing sulfur doubly bonded to a singlecarbon atom and SH linkages bonded to a carbon atom which does notreadily react with metallic silver and which forms a light-inert silvercomplex by reaction with undeveloped silver halide, only until thesilver halide has been substantially completely converted to a complexwith said compound, said solution containing a metal below silver andabove osmium in the electromotive series, leaving said complex in saidlayer and drying said stabilized image without any further treatment.

6. A rapid process for the formation of an image in a hardened silverhalide photographic layer which comprises exposing said layer,developing it with a silver halide developing agent and stabilizing itby treatment with a solution of thiourea containing gold chloride, onlyuntil the unexposed silver halide is substantially completely convertedto a light inert silver complex by reaction with the stabilizingmaterial, and drying said stabilized image without any furthertreatment.

'7. A rapid process for the formation of an image in a hardened silverhalide photographic layer which comprises exposing said layer,developing it with a silver halide developing agent and stabilizing itby treatment with a solution of ammonium thiosulfate containing goldchloride, only until the unexposed silver halide is substantiallycompletely converted to a light inert silver complex by reaction withthe stabilizing material, and drying said stabilized image without anyfurther treatment.

8. A rapid process for the formation of an image in a hardened silverhalide photographic layer which comprises exposing said layer,developing it with a silver halide developing agent and stabilizing itby treatment with a solution of ammonium thiosulfate containing goldchloride and a hydroxy aliphatic amine, only until the unexposed silverhalide is substantially completely converted to a light inert silvercomplex by reaction with the stabilizing material, and

drying said stabilized image without any further treatment.

HAROLD D. RUSSELL.

REFERENCES CITED The following references are of record in the file ofthis patent;

UNITED STATES PATENTS Number Name Date 1,356,236 sulzberger Oct. 19,1920 1,361,352 Sulzberger Dec. '7, 1920 FOREIGN PATENTS Number CountryDate 611,228 Germany Mar. 23, 1935

